An open comparative study was undertaken in order to assess the efficacy and safety of a single dose of azithromycin in the treatment of community-acquired atypical pneumonia. A total of 100 adult patients with atypical pneumonia syndrome were randomized to receive 1.5 g of azithromycin as a single dose, or 500 mg once daily for 3 days. The presence of Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia psittaci, Coxiella burnetii, and Legionella pneumophila infection was diagnosed by serological tests. Control clinical examinations were performed 72 h, 10-12 days and 4 weeks after treatment initiation. Among 96 patients (48 in each group) who were evaluable for clinical efficacy M. pneumoniae infection was confirmed in 24, C. pneumoniae in nine, C. psittaci in five, C. burnetii in six, and L. pneumophila in five. Forty-seven patients (97.9%) in each group were cured. Side effects were observed in two patients in the single-dose group, and one patient in the 3-day group. In conclusion, a single 1.5 g dose of azithromycin may be an alternative to the standard 3-day azithromycin regimen in the treatment of outpatients with atypical pneumonia syndrome.